Threaded tubular connection provided with a metallic coating on the threading and on the sealing surface

ABSTRACT

A threaded tubular connection for drilling or operating hydrocarbon wells contains a portion of a tubular element with a male end having an axis of revolution and provided with a first threading extending about the axis of revolution, the male end portion being complementary with a portion of a tubular element with a female end having an axis of revolution and provided with a second threading extending about the axis of revolution, the male and female end portions being capable of being connected by makeup, each of the male and female end portions further comprising a sealing surface with a metal-metal interference, wherein the threading and the sealing surfaces of the male and female end portions are coated with a metallic anti-corrosion and anti-galling layer wherein zinc (Zn) is the major element by weight. One of the metallic anti-corrosion and anti-galling layers is coated with a passivation layer and the other is at least partially coated with a lubricant layer.

FIELD OF THE INVENTION

The present invention relates to a tubular element for drilling and/oroperating a hydrocarbon well, and more precisely to the threaded end ofan element of this type. This end may be male or female in type, and iscapable of being connected to a corresponding end of an analogouselement in order to form a joint or connection.

The invention also relates to a threaded connection resulting fromconnecting two tubular elements by makeup, one of which may be acoupling with two female ends.

The term “tubular element for drilling and operating a hydrocarbon well”means any element with a substantially tubular shape which can beconnected to another element which may or may not be of the same type,with a particular view of constituting either a hydrocarbon well drillstring or a work-over riser or operating this kind of string such as ariser, or a casing or tubing string used in operating a well. Theinvention is also applicable to the elements used in a drill string suchas, for example, drill pipes, heavy weight drill pipes, drill collarsand tool joints.

Each tubular element comprises an end portion with a male threaded zoneor a female threaded zone which is intended to be made up with acorresponding end portion of an analogous element. When connected, theelements compose what is known as a joint or connection.

These threaded tubular components of a connection are connected underpre-defined loads in order to respond to the clamping and seal demandsimposed by the conditions of use; more precisely, a pre-defined torqueis aimed for. Further, it should be known that the threaded tubularcomponents may have to undergo several cycles of makeup and breakout, inparticular in service.

The conditions for use of these threaded tubular components give rise todifferent types of loads. They have been reduced, inter alia, by usingfilms or greases on the sensitive parts of these components such as thethreaded zones, the abutment zones or indeed the metal/metal sealingsurfaces.

Induced constraints in particular include constraints due to being keptin storage, necessitating the application of storage greases (differentfrom makeup greases applied before being put into service). However,other solutions exist, consisting of using organic coatings.

Thus, makeup operations are usually carried out under a high axial load,for example because of the weight of a tube several metres long to beconnected via the threaded connection, possibly aggravated by a slightmisalignment of the axis of the threaded elements to be connected. Thisinduces risks of galling in the threaded zones and/or in the metal/metalsealing surfaces. Thus, the threaded zones as well as the metal/metalsealing surfaces are routinely coated with lubricants.

Furthermore, the threaded tubular components are often stored then madeup in an aggressive environment. This is the case, for example, in an“offshore” situation in the presence of a saline mist, or in an“onshore” situation in the presence of sand, dust and/or otherpollutants. Thus, it is necessary to employ different types of coatingagainst corrosion on the surfaces which are loaded during makeup, whichis the case with the threaded zones or indeed in zones in clampingcontact, which is the case with the metal/metal sealing surfaces and theabutments.

However, having regard to environmental standards, it appears that usinggreases complying with the standard API RP 5A3 (American PetroleumInstitute) does not constitute a long-term solution, since such greasesare caused to be extruded from the tubular components and released intothe environment or into the well, causing blockages which necessitatespecial cleaning operations

In order to respond to the problems of a long-lasting resistance tocorrosion, galling and to prerogatives associated with environmentalconsiderations, an alternative to greases has been developed. They notonly provide a response to corrosion resistance performance and gallingperformance, but also to the industrial constraints involved infabricating threaded ends.

Since 1969, WHITFORD (registered trade mark) has proposed highperformance coatings produced from a mixture of polyamide-imide resinand fluoropolymers for threaded fasteners, which necessitate adaptingthe friction in rapid makeup/breakout operations.

Furthermore, since 2002, in the context of threaded connections,coatings based on polyamide-imide resin have been proposed to lubricateand guarantee the resistance to galling during makeup, as described indocuments EP 1 378 698 and EP 1 959 179.

That prior art principally proposes obtaining dry films from apolyamide-amic acid precursor dissolved in a polar solvent or in anethanol/toluene mixture. The dry film is generally applied in order toensure lubrication as a function of the contact pressures in thethreading. The proportion of fillers is relatively high, with apigment/binder weight ratio in the range 0.25 to 4, preferably more than3. The dry film is thus advantageously sacrificial and sufficientlyresistant to wear during functioning of the solid lubricant.

Application WO 2004/033951 concerns a threaded metallic tube for the oilextraction industry with a threaded end portion the surface of which istreated and in which the metallic surface has a surface roughness (Ra)in the range 2.0 μm to 6 μm, this surface being covered with a uniformlayer of a dry anti-corrosion coating and with a second, uniform layerof a dry lubricant coating. Alternatively, the two layers may becombined into a single layer of a dry anti-corrosion coating comprisinga dispersion of particles of dry lubricant. Nevertheless, the dispersionof particles over the anti-corrosive layer deposited on the substrateintroduces a certain amount of heterogeneity.

In addition, the application EP 2 128 506 concerns a threaded connectionof the male/female type for steel tubes having a contact surfacecomprising a threaded portion and a non-threaded metal-on-metal contactportion. The surface of at least one of the male or female elements iscoated with a first laminating layer produced from a Cu—Zn alloy or aCu—Zn-M1 alloy (where M1 is at least one element selected from Sn, Biand In). In spite of the interesting results with these layerscontaining copper, the anti-corrosive properties associated with themhave been shown to have limits which it would be desirable to overcome.

Thus, the corrosion and galling behaviour of those disclosures could beimproved by proposing, in addition to the functional properties ofcorrosion performance and good galling resistance, and a seal to gas andto liquid for the connections of the invention disclosed below. Based onthis concept, the present invention proposes coating a threaded elementor a connection formed by connecting threaded elements intended fordrilling and/or operating hydrocarbon wells.

DISCLOSURE OF THE INVENTION

In a first aspect, the invention pertains to a threaded portion of atubular element for a threaded tubular connection for drilling oroperating hydrocarbon wells, having an axis of revolution, said portioncomprising a threading extending over its outer or inner peripheralsurface, and a first sealing surface on said peripheral surface, saidfirst sealing surface being capable of producing metal-metalinterference with a corresponding second sealing surface belonging to acomplementary threaded portion of a tube, characterized in that saidthreading and said first sealing surface are coated with a metallicanti-corrosion and anti-galling layer wherein zinc (Zn) is the majorelement by weight.

Preferably, the metallic anti-corrosion and anti-galling layer isdeposited electrolytically.

Preferably, the metallic anti-corrosion and anti-galling layer containsat least 50% by weight of zinc (Zn).

Preferably, the metallic anti-corrosion and anti-galling layer has athickness in the range 4 μm to 20 μm.

Preferably, the metallic anti-corrosion and anti-galling layer comprisesa substance selected from the group constituted by pure zinc (Zn) and abinary alloy of zinc (Zn) of the type Zn—X, in which X is selected fromnickel (Ni), iron (Fe), magnesium (Mg) and manganese (Mn). Preferably,the metallic anti-corrosion and anti-galling layer is a zinc-nickel(Zn—Ni) alloy wherein the nickel (Ni) content is in the range 12-15% byweight and wherein the microstructure is monophase and in the gamma (γ)phase.

Preferably, the metallic anti-corrosion and anti-galling layer is coatedwith a lubricant layer comprising a resin and a dry solid lubricantpowder dispersed in said resin.

Preferably, the metallic anti-corrosion and anti-galling layer is coatedwith a passivation layer comprising trivalent chromium (Cr(III)), saidpassivation layer being formed between the metallic layer and thelubricant layer.

Preferably, the metallic anti-corrosion and anti-galling layer is coatedwith a passivation layer comprising trivalent chromium (Cr(III)).

Preferably, the passivation layer is coated with a barrier layerconstituted by a mineral matrix layer comprising particles of silicondioxide (SiO₂).

Preferably, the passivation layer is coated with a barrier layerconstituted by an organo-mineral matrix layer comprising particles ofsilicon dioxide (SiO₂).

Preferably, the portion further comprises a first abutment which iscapable of coming into contact, at the end of makeup, with acorresponding second abutment and belonging to a complementary threadedtube portion.

Preferably, the threaded portion is produced from steel.

In an alternative, the threaded portion is male in type, with athreading extending over its outer peripheral surface as well as a firstsealing surface on said outer peripheral surface.

In another alternative, the threaded portion is female in type, with athreading extending over its inner peripheral surface as well as a firstsealing surface on said inner peripheral surface.

In a second aspect, the invention pertains to a threaded portion of atubular element for a threaded tubular connection for drilling oroperating hydrocarbon wells, having an axis of revolution, said portioncomprising a threading extending over its outer or inner peripheralsurface, and a first sealing surface on said peripheral surface, saidfirst sealing surface being capable of producing metal-metalinterference with a corresponding second sealing surface belonging to acomplementary threaded portion, characterized in that said threading andsaid first sealing surface are coated with a metallic anti-galling layerwherein zinc (Zn) is the major element by weight, said metallicanti-galling layer being at least partially coated with a lubricantlayer comprising a resin and a dry solid lubricant powder dispersed insaid resin.

In a preferred manner, the metallic anti-galling layer in this threadedportion is deposited electrolytically.

In a preferred manner, the metallic anti-galling layer contains at least50% by weight of zinc (Zn).

In a preferred manner, the metallic anti-galling layer has a thicknessin the range 4 μm to 20 μm.

In a preferred manner, the lubricant layer has a thickness in the range5 μm to 50 μm.

In a preferred manner, the metallic anti-galling layer comprises asubstance selected from the group constituted by pure zinc (Zn) and abinary alloy of zinc (Zn) of the type Zn—X, in which X is selected fromnickel (Ni), iron (Fe), magnesium (Mg) and manganese (Mn). In apreferred manner, the metallic anti-galling layer is a binaryzinc-nickel (Zn—Ni) alloy wherein the nickel (Ni) content is in therange 12-15% by weight and wherein the microstructure is monophase andin the gamma (γ) phase.

In a preferred manner, the threaded portion of the invention comprises apassivation layer comprising trivalent chromium (Cr(III)), saidpassivation layer being formed between the metallic anti-galling layerand the lubricant layer.

In a preferred manner, the dry solid lubricant powder is selected fromthe group constituted by polytetrafluoroethylenes (PTFE), molybdenumdithiocarbamates (MoDTC), molybdenum disulphides (MoS₂), carbon blacks(C), graphite fluorides (CF_(x)) or a mixture thereof.

In a preferred manner, the resin is selected from the group constitutedby polyvinyl resins, epoxy resins, acrylic resins, polyurethane resinsand polyamide-imide resins.

In a preferred manner, the resin is of the acrylic type and the drysolid lubricant powder contains 3% to 15% of carbon blacks, MoS₂ ormolybdenum dithiocarbamates (MoDTC), alone or in combination.

In a preferred manner, the threaded portion of the invention furthercomprises a first abutment which is capable of coming into contact, atthe end of makeup, with a corresponding second abutment belonging to acomplementary threaded portion.

In a preferred manner, the threaded portion is produced from steel.

In one case, the threaded portion is male in type, with a threadingextending over its outer peripheral surface, as well as a first sealingsurface on said outer peripheral surface.

In another case, the threaded portion of the invention is female intype, with a threading extending over its inner peripheral surface aswell as a first sealing surface on said inner peripheral surface.

In a third aspect, the invention pertains to a threaded tubularconnection for drilling or operating hydrocarbon wells, comprising aportion of a tubular element with a male end having an axis ofrevolution and provided with a first threading extending about the axisof revolution, said male end portion being complementary with a portionof a tubular element with a female end having an axis of revolution andprovided with a second threading extending about the axis of revolution,said male and female end portions being capable of being connected bymakeup, each of the male and female end portions further comprising asealing surface with a metal-metal interference, characterized in thatthe threading and the sealing surface of one of the two, male or female,end portions are coated with a first metallic anti-corrosion andanti-galling layer wherein zinc (Zn) is the major element by weight,said first metallic anti-corrosion and anti-galling layer being coatedwith a first passivation layer, the threading and sealing surface of themale or female complementary portion being coated with a second metallicanti-galling layer wherein zinc (Zn) is the major element by weight,said second metallic anti-galling layer being at least partially coatedwith a lubricant layer comprising a resin and a dry solid lubricantpowder dispersed in said resin.

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second metallic layers is depositedelectrolytically.

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second metallic layers contains atleast 50% by weight of zinc (Zn).

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second metallic layers has athickness in the range 4 μm to 20 μm.

Preferably, the lubricant layer has a thickness in the range 5 μm to 50μm.

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second metallic layers comprises asubstance selected from the group constituted by pure zinc (Zn) and abinary alloy of zinc (Zn) of the type Zn—X, in which X is selected fromnickel (Ni), iron (Fe), magnesium (Mg) and manganese (Mn).

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second metallic layers is a binaryzinc-nickel (Zn—Ni) alloy wherein the nickel (Ni) content is in therange 12-15% by weight and wherein the microstructure is monophase andin the gamma (γ) phase.

Preferably, the first passivation layer comprises trivalent chromium(Cr(III)).

Preferably, the threaded tubular connection of the invention is suchthat a second passivation layer comprising trivalent chromium (Cr(III))is formed between the second metallic anti-galling layer and thelubricant layer.

Preferably, the dry solid lubricant powder is selected from the groupconstituted by polytetrafluoroethylenes (PTFE), molybdenum disulphides(MoS₂), molybdenum dithiocarbamates (MoDTC), carbon blacks (C), graphitefluorides (CF_(x)) or a mixture thereof.

Preferably, the threaded tubular connection in accordance with theinvention is such that the resin is selected from the group constitutedby polyvinyl resins, epoxy resins, acrylic resins, polyurethane resinsand polyamide-imide resins.

Preferably, the resin is of the acrylic type and the dry solid lubricantpowder contains 3% to 15% of carbon blacks, MoS₂, or molybdenumdithiocarbamates (MoDTC), alone or in combination.

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second passivation layers is coatedwith a barrier layer constituted by a mineral matrix layer comprisingparticles of silicon dioxide (SiO₂).

Preferably, the mineral matrix layer further comprises potassium oxide.

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second passivation layers is coatedwith a barrier layer constituted by an organo-mineral matrix layercomprising particles of silicon dioxide (SiO₂).

Preferably, the threaded tubular connection of the invention is suchthat at least one of the first and second passivation layers is coatedwith a layer of dry lubricant.

Preferably, the male end portion in accordance with the inventionfurther comprises a first abutment and the female end portion furthercomprises a second abutment, the first and second abutments beingcapable of coming into contact with each other at the end of makeup.

Preferably, the threaded tubular connection in accordance with theinvention is such that the male and female end portions are producedfrom steel.

DESCRIPTION OF THE FIGURES

FIG. 1A represents a close-up view of a coated surface of a femalethreaded tube end, in section along the longitudinal axis, in a firstembodiment in accordance with the invention.

FIG. 1B represents a close-up view of a coated surface of a malethreaded tube end, in section along the longitudinal axis, in the firstembodiment in accordance with the invention.

FIG. 2A represents a close-up view of a coated surface of a femalethreaded tube end, in section along the longitudinal axis, in a secondembodiment in accordance with the invention.

FIG. 2B represents a close-up view of a coated surface of a malethreaded tube end, in section along the longitudinal axis, in the secondembodiment in accordance with the invention.

FIG. 3A represents a close-up view of a coated surface of a femalethreaded tube end, in section along the longitudinal axis, in a thirdembodiment in accordance with the invention.

FIG. 3B represents a close-up view of a coated surface of a malethreaded tube end, in section along the longitudinal axis, in the thirdembodiment in accordance with the invention.

FIG. 4A represents a close-up view of a coated surface of a femalethreaded tube end, in section along the longitudinal axis, in a fourthembodiment in accordance with the invention.

FIG. 4B represents a close-up view of a coated surface of a malethreaded tube end, in section along the longitudinal axis, in the fourthembodiment in accordance with the invention.

FIG. 5A represents a close-up view of a coated surface of a femalethreaded tube end, in section along the longitudinal axis, in a fifthembodiment in accordance with the invention.

FIG. 5B represents a close-up view of a coated surface of a malethreaded tube end, in section along the longitudinal axis, in the fifthembodiment in accordance with the invention.

FIG. 6A shows a comparative photograph of a threaded element inaccordance with a prior art threaded element.

FIG. 6B shows a comparative photograph of a threaded element inaccordance with a prior art threaded element.

FIG. 6C shows a comparative photograph of a threaded element inaccordance with the invention.

FIG. 6D shows a comparative photograph of a threaded element inaccordance with the invention.

FIG. 7 shows a photograph of a threaded element in accordance with anembodiment of the invention.

EMBODIMENTS

The invention will be better understood from the following descriptionwhich provides non-limiting explanations. It should be noted that thesubstrate onto which the various layers in accordance with the inventionare deposited is preferably formed from steel and that the invention mayequally be performed on a male as on a female end.

The threaded portion of the invention systematically comprises athreading which extends over its outer or inner peripheral surfacedepending on whether the threaded portion is respectively male orfemale, and a first sealing surface on said peripheral surface, saidfirst sealing surface being capable of producing metal-metalinterference with a corresponding second sealing surface belonging to acomplementary threaded portion. The sealing surface is important in thethreaded portion in accordance with the invention because, when coatedin accordance with the invention, it provides a seal to gas and toliquid with the metal/metal contact. Preferably, the metal/metal contactis produced with an interference.

In the description below, the layers are deposited on at least thethreading of the threaded portion in accordance with the invention andon the sealing surface.

In accordance with the invention, a metallic layer wherein zinc (Zn) isthe major element by weight will be deposited on the substrate of thetubular threaded portion, preferably formed from steel. The metalliclayer in accordance with the invention is ideally depositedelectrolytically. The principle of this type of deposit is summarizedbelow. Apart from its mechanical strength, the major advantage of themetallic layer is its microstructural uniformity. It should beunderstood here that “microstructural uniformity” does not necessarilyimply a monophase crystalline structure; in contrast, the reverse istrue.

In the context of the invention, the term “metallic layer” means a layerconstituted by metal. Clearly, impurities may be present, butpreferably, the layer is exclusively metallic. The exclusively metalliclayer of the invention has the advantage of having a microstructuraluniformity. In fact, under the optical microscope with a magnificationof ×500, the observed microstructure has a homogeneous appearance.

In fact, both the mechanical strength and the microstructural uniformityof the metallic layer are substantially greater than those of organiccoatings which, furthermore, have poorer stability to temperature.

Deposition by electrolysis is a technique used here to reduce metallicions or oxides into pure metals by applying an electric current densitywhich may be from 1 amp/dm² to 100 amp/dm² in the context of theinvention. The electrolytic bath is at a temperature in the range 18° C.to 50° C. Below 18° C., the efficiency of the bath is insufficient.Above 50° C., the chemical components (for example additives) of thebath will be degraded. As an example, a method for depositing a metalliccoating known as buffer electrolysis may require very high currents atthe high end of the range cited above.

The electrolytes are necessary in order to provide the electricalconductivity and may be aqueous solutions or molten salts. A metalliclayer wherein zinc (Zn) is the major element by weight may be depositedelectrolytically; this is the technique used in the invention. Othermetals such as copper or even nickel may also be depositedelectrolytically.

Electrolysis in an aqueous medium is carried out with a system of twoelectrodes composed of an anode and a cathode. Ion reduction occurs atthe cathode and is defined as follows:M^(n+) +ne ⁻↔M, where M represents a metal and n is a whole number.

In the case of electro-deposition, the cathode is the substrate ontowhich deposition occurs. In fact, ideally, this is a steel in the caseof the invention.

At the anode, the reaction obtained is an oxidation of water to formgaseous dioxygen in accordance with the two equations below, dependingon whether the medium is respectively acidic or alkaline:2H₂O→O_(2(g))+4H⁺+4e ⁻  (1)or6OH⁻→3H₂O+3/2O_(2(g))+6e ⁻.  (2)

One of the principal difficulties with electrolysis in an aqueous mediumis the competition that exists between reduction of the metallic ionsand reduction of the solvent at the cathode, defined by the reaction:2H₂O+2e ⁻→H_(2(g))+2OH⁻.  (3)

In theory, the reactions which should take place are linked to thepotentials of the electrodes which are themselves linked to eachselected material, but experiments carried out in the context of theinvention produced results which were difficult to predict. In fact, thekinetics of the reactions is complex.

The work Modern Electroplating, John Wiley & Sons, Inc. 5^(th) edition,p. 285-307, section 10: Electrodeposition of zinc and zinc alloys, R.Winand, 2010 provides more details regarding the electrolytic depositionof zinc or an alloy of zinc onto substrates.

The deposition of a metallic layer wherein zinc (Zn) is the majorelement by weight in accordance with the invention onto the substrate,preferably steel, means that both the corrosion behaviour, the gallingresistance and the mechanical strength of the assembly can be modifiedat the same time. The presence of a deposit of an alloy with an elementother than zinc (Zn) as the major element, i.e. having the highestcontent by weight of the elements of the alloy, is not desirable becausethe corrosion behaviour performances are such that the desired effect isnot obtained. The thickness of the metallic layer wherein zinc (Zn) isthe major element by weight is preferably in the range 4 to 20 μm. Below4 μm, the anti-corrosion effect is reduced because the layer runs therisk of exhibiting insufficient corrosion behaviour. Above 20 μm, thereis a high risk of the accumulation of H₂ by combination of H⁺ inaccordance with equation (1). This accumulation is higher when the layeris thicker. There is then the danger that H₂ gas will be trapped in thestructure, which will become more fragile due to the generation ofinternal stresses. Still more preferably, the thickness of the metalliclayer is in the range 6 to 15 μm.

The metallic layer wherein zinc (Zn) is the major element by weight,deposited electrolytically, may be completed by additional treatmentssuch as the formation of a passivation layer on the metallic layer. In avariation, it is also possible to deposit, over the whole of themetallic layer or over a portion thereof, a lubricant layer comprising aresin and a dry solid lubricant powder dispersed in this resin. Inaddition to its lubricating function, this layer may contribute to theanti-corrosion function. It is entirely possible in the context of theinvention to deposit a lubricant layer of this type on the passivationlayer. The lubricant layer has a thickness in the range 5 μm to 50 μm.Below 5 μm, the lubricating effect is not satisfactory. Above 50 μm, themaximum makeup torque may become too high. Furthermore, above 50 μm,there is the danger that chips originating from the damaged coatingmight be formed. Chips of this type might fall to the bottom of the oilwell and consequently cause the operating conditions to deteriorate.Preferably, the lubricant layer has a thickness in the range 10 μm to 30μm.

Other variations consist of depositing a barrier layer generally knownas a sealer onto the formed passivation layer.

Another variation also consists of depositing a lubricant layer on theentire passivation layer which has been formed, or onto just a portionthereof.

It is also entirely possible to deposit a lubricant layer, with orwithout an anti-corrosion function, onto the metallic layer in itsentirety or onto just a portion thereof without having formed apassivation layer.

The various layers in the various configurations of the invention aredeposited by means of successive operations carried out on thepreferably metallic substrate, or even more preferably onto steel. Thefollowing operations are carried out: chemical or electrochemicaldegreasing of the substrate using solvents and/or alkaline solutions,followed by rinsing. Next, chemical or electrochemical stripping of thesurface of the substrate is carried out, preferably by immersing thesubstrate in an acidic solution in order to eliminate the surfaceoxides.

The surface may be activated using the following products: hydrochloricacid, sulphuric acid, phosphoric acid, nitric acid, hydrofluoric acid ora mixture of these acids.

In accordance with the invention, a metallic layer wherein zinc (Zn) isthe major element by weight is deposited onto the threaded end portioncomprising a threading and a first sealing surface. This means that thedeposit of the metallic layer, ideally carried out by electrolysis, maybe: zinc (Zn) alone or a binary alloy of zinc (Zn) of the type Zn—X, inwhich X is selected from nickel (Ni), iron (Fe), magnesium (Mg) andmanganese (Mn).

Pure Zn will be used for its anti-corrosion and anti-gallingcharacteristics. In accordance with the invention, a metallic layerwherein zinc (Zn) is the major element by weight is used because,compared with iron, in the context of a steel type substrate, zinc has amore negative standard potential. In other words, Zn offers effectivecathodic protection against corrosion in this case.

In the context of a steel type substrate, using pure Zn is thus notproblematic, but Zn—Ni is preferred because pure Zn is consumed(chemically eroded) at a higher rate. Thus, a particularly thick layerwould be required, which is not advantageous on the threading and thesealing surface. In fact, a thick layer would result in a smallerclearance at the threads, which would impair optimization of the contactsurfaces which would be preferred to be made, depending on the type ofconnection. Zn—Ni should be used, not just for its anti-corrosioncharacteristics, but also for its anti-galling characteristics.

Zn—Fe is also a sacrificial protection as regards the preferred steeltype substrate. The layer of Zn—Fe is a good adhesion promoter. Zn—Feproduces a lower corrosion rate than pure Zn.

Zn—Mg is of interest, because this alloy slows down the rate ofcorrosion due to the presence of Mg in the case of a preferredsubstrate, i.e. steel.

In the context of a steel type substrate, Zn—Mn provides barrierprotection. However, the barrier function is of advantage in terms ofanti-corrosion resistance because it will not be attacked and willremain intact. Furthermore, it has very good corrosion behaviour whennaturally exposed.

It will be recalled that electrolytic deposition can be used to improvethe uniformity of the deposit from a microstructural viewpoint. Clearly,other manners of depositing a metallic coating exist, such asgalvanization, spraying, or even sherardizing.

The alternative, consisting of forming a passivation layer on themetallic layer, means that the corrosion resistance can be furtherimproved.

The alternative, consisting of depositing a lubricant layer comprising aresin and a dry solid lubricant powder dispersed in said resin over atleast a part of the portion, means that the makeup torque of theconnection can be better controlled and galling can be avoided.

The dry solid lubricant powder is preferably selected from the groupconstituted by polytetrafluoroethylenes (PTFE), molybdenum disulphides(MoS₂), carbon blacks (C), graphite fluorides (CF_(x)) or a mixturethereof.

PTFEs (polytetrafluoroethylenes) provide lubricating properties with acoefficient of friction which is stable with contact pressure. Themakeup torque is thus better controlled. The mean particle size of thePTFE particles of the invention is less than 15 μm. Above 15 μm, thedispersion in the resin would be heterogeneous because the particleswould be too thick compared with the total thickness of the lubricantlayer.

The resin is selected from the group constituted by polyvinyl resins,epoxy resins, acrylic resins, polyurethane resins and polyamide-imideresins.

The polyvinyl resins, epoxy resins and acrylic resins adhere in asatisfactory manner to the metallic layer containing Zn or thepassivation layer.

Polyurethane resins have the advantage of being particularly stablechemically and are easy to employ by curing.

Polyamide-imide resins are particularly resistant to wear.

In a preferred embodiment, the resin is acrylic in type and the drysolid lubricant powder dispersed in said resin contains 3% to 15% ofcarbon blacks, MoS₂, or molybdenum dithiocarbamates (MoDTC), alone or incombination. This combination exhibits a synergistic effect in terms ofanti-galling, adhesion and control of the makeup torque.

The molybdenum disulphides (MoS₂), molybdenum dithiocarbamates (MoDTC),carbon blacks (C), graphite fluorides (CF_(x)) or a mixture thereofsupply lubricating properties with a coefficient of friction which isstable with contact pressure. The makeup torque is thus bettercontrolled.

Derivatives of MoS₂ also have all of the lubricating properties citedabove.

In a preferred embodiment, the deposited layers of metal containing Znare a binary Zn—Ni alloy containing between 12% and 15% of Ni, theremainder clearly being Zn and inevitable impurities wherein the sum ofthe quantities is strictly less than 3% by weight. In fact, below 12% ofNi, the corrosion resistance is not optimized, while above 15% ofnickel, the structure of the coating is no longer monophase butpolyphase, and the phases present induce internal stresses and renderthe coating fragile.

Finally, the microstructure of this preferred metallic deposit of Zn—Niwith 12% to 15% of nickel is preferably of the monophase type and thephase which is present is gamma in type. This gamma type crystallinestructure ensures better corrosion resistance.

Preferably, the passivation layer comprises trivalent chromium Cr(III).This trivalent chromium is more stable than Cr(II) and not harmful tohealth, unlike Cr (VI).

Preferably, the passivation layer, when it is present, is coated with abarrier layer constituted by a mineral matrix layer comprising particlesof silicon dioxide (SiO₂). This barrier layer improves theanti-corrosion resistance.

An alternative consists of using a passivation layer coated with abarrier layer constituted by an organo-mineral matrix layer comprisingparticles of silicon dioxide (SiO₂). This barrier layer improves theanti-corrosion resistance.

One embodiment consists of depositing a lubricant layer onto thepassivation layer in order to better control the makeup torque of theconnection and to avoid galling.

The metal/metal contact of the threaded portions of the invention ismade with an interference. The “interference” between the male andfemale elements of the invention corresponds to a diametricalinterference between coupled points of the two surfaces of revolution.More particularly, this diametrical interference is defined by thedifference in the diameter of the regular section of the surfaces at thecoupled points of the two surfaces of revolution. This difference may bemeasured before assembling said elements, then may be evaluated at thecontact surface when the two elements have been assembled with eachother. In practice, it is a routine matter to ensure that one diameterof a portion of the outer peripheral surface of the male element isslightly greater than the diameter of a portion of the inner peripheralsurface of the female element. This brings about an exchange of materialin the contact zone of these surfaces. Thus, a high contact pressure isprovided between said coupled points.

EXAMPLES

The non-limiting examples of threaded portions (either male or female orboth) formed from steel described below were treated electrolyticallywith a binary zinc-nickel alloy. The binary zinc-nickel alloy used inthe examples is available from ELECTROPOLI (registered trade mark) underthe commercial name ZELTEC 2.4 (registered trade mark).

The parameters for the electrolytic treatment were as follows:

-   -   temperature of electrolytic bath: Temp.=36° C.;    -   pH of electrolytic bath: pH=5.4;    -   applied current density: J=2 A/dm²;    -   dwell time in electrolytic bath: t=20 min.

Thus, the electrolytic treatment was carried out in an acidic medium.

This produced a metallic layer comprising zinc (Zn). The thickness ofthe metallic layer was in the range 4.0 μm to 12.5 μm (extreme values),typically 6 μm to approximately 8 μm. The nickel (Ni) content wasgenerally in the range 12% to 15% (extreme values). It followed that thezinc (Zn) content was generally in the range 85% to 88% (extremevalues). The metallic layer had both anti-galling and anti-corrosionproperties.

When a barrier layer was present, it was in particular the product soldunder the name FINIGARD 460 from COVENTYA (registered trade mark).

When a passivation layer was present, it was in particular the productsold under the name FINIDIP 128 CF (cobalt free) from COVENTYA(registered trade mark). It could also be the product sold under thename EcoTri (registered trade mark) NoCo from ATOTECH (registered trademark) Deutschland GmbH. These two products have the particular advantageof being free of hexavalent chromium (Cr(VI)).

In the exemplary embodiments described below, each threaded portion isintended to form a portion of a threaded tubular connection. Eachthreaded portion has an axis of revolution and comprises a threading.The threading extends over the outer peripheral surface of the threadedportion when it is a male element; in contrast, the threading extendsover the inner peripheral surface of the threaded portion when it is afemale element. Each threaded portion also comprises a first sealingsurface on the peripheral surface which is arranged to producemetal-metal interference with a corresponding second sealing surfacebelonging to a complementary threaded portion of a tube. A complementarythreaded portion of a male portion is a female threaded portion. Acomplementary threaded portion of a female portion is a male threadedportion.

In the exemplary embodiments below, reference is systematically made toan assembly of two complementary threaded portions which can form atubular connection when they are made up one into the other. It shouldbe understood that the surface treatments, the layers and the finishingtreatments may be applied irrespectively to a male threaded portion orto a female threaded portion. As a consequence, when an embodiment makesreference to a male portion comprising a certain particular firstcoating (ensemble of layers) and makes reference to a female portioncomprising a certain particular second coating (other ensemble oflayers), it should be understood that it is possible to reverse theparticular first and second coatings of the threaded portions, i.e.apply the first particular coating to the female portion and apply thesecond particular coating to the male portion.

Example 1

FIG. 1 shows a substrate 100 formed from steel. The substrate 100 isshaped so as to form a female threaded portion 102 and a male threadedportion 104.

The male threaded portion 104 is coated with a first anti-corrosion andanti-galling layer 108. The first metallic layer 108 is depositedelectrolytically, as described above. The first metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely in a mean amount of 85.7%. The first metallic layer 108 hasa mean thickness of 8.3 μm. Furthermore, the first metallic layer has amonophase gamma type microstructure.

The first metallic layer 108 is coated with a passivation layer 110, asdescribed above. By definition, the passivation layer has anti-corrosiveproperties.

Optionally, the passivation layer 110 is coated with a barrier layer 114as described above, which also has anti-corrosive properties.

The female threaded portion 102 is coated with a second metallicanti-galling layer 106. The second metallic layer 106 is constituted bya binary Zn—Ni alloy.

The second metallic layer 106 is deposited electrolytically. The secondmetallic layer 106 contains mainly zinc (Zn) by weight. Furthermore, thesecond metallic layer has a monophase gamma type microstructure.

The second metallic layer 106 is coated with a lubricant layer 112. Inthe embodiment of FIG. 1, the lubricant layer 112 is of the hot-melttype, having both lubricating properties and anti-corrosive properties.

The hot-melt lubricant layer has the following composition by weight:

matrix: 70% to 95%

solid lubricant: 5% to 30%.

The matrix has the following composition:

homopolymeric polyethylene: 8% to 90%

carnauba wax: 5% to 30%

zinc stearate: 5% to 30%

calcium sulphonate derivative: 0 to 50%

alkyl polymethacrylate: 0 to 15%

colorant: 0 to 1%

antioxidant: 0 to 1%

Silicone (surfactant element): 0 to 2%

Example 2

FIG. 2 shows a substrate 100 formed from steel. The substrate 100 isshaped so as to form a female threaded portion 102 and a male threadedportion 104.

The male threaded portion 104 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 is depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.5%. The first metal layer 108 has amean thickness of 6.7 μm.

The metallic layer 108 of the male threaded portion 104 is coated with apassivation layer 110, as described above. By definition, thepassivation layer has anti-corrosive properties.

The passivation layer 110 of the male threaded portion 104 is coatedwith a barrier layer 114 as described above, which also hasanti-corrosive properties.

The female threaded portion 102 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 is depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.4%. The metallic layer 108 has a meanthickness of 7.4 μm.

The metallic layer 108 of the female threaded portion 102 is coated witha passivation layer 110, as described above. By definition, thepassivation layer has anti-corrosive properties.

The passivation layer 110 of the female threaded portion 102 is coatedwith a lubricant layer 112. In the embodiment of FIG. 2, the lubricantlayer 112 is of the hot-melt type having both lubricating properties andanti-corrosive properties.

Example 3

FIG. 3 shows a substrate 100 formed from steel. The substrate 100 isshaped so as to form a female threaded portion 102 and a male threadedportion 104.

The male threaded portion 104 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.5%. The first metallic layer 108 has amean thickness of 7 μm.

The metallic layer 108 of the male threaded portion 104 is coated with apassivation layer 110, as described above. By definition, thepassivation layer has anti-corrosive properties.

The passivation layer 110 of the male threaded portion 104 is coatedwith a barrier layer 114 as described above, which also hasanti-corrosive properties.

The substrate 100 of the female threaded portion 102 has a surfaceroughness. The surface roughness has been obtained by a sand blastingprocess. A sand blasting process in particular enabled a surfaceroughness (Ra) in the range 1.0 μm to 10 μm to be produced. In theexemplary embodiment of FIG. 3, the surface roughness (Ra) isapproximately 2 μm.

The female threaded portion 102 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 85.6%. The metallic layer 108 has a meanthickness of 7 μm.

The metallic layer 108 of the female threaded portion 102 is coated witha passivation layer 110, as described above. By definition, thepassivation layer has anti-corrosive properties.

The passivation layer 110 of the female threaded portion 102 is coatedwith a lubricant layer 112. In the embodiment of FIG. 3, the lubricantlayer 112 comprises a resin and a dry solid lubricant dispersed in thisresin. In this case, the lubricant layer 112 is constituted by apolyurethane resin (type PU2K) in which particles of carbon black havebeen dispersed.

Example 4

FIG. 4 shows a substrate 100 formed from steel. The substrate 100 isshaped so as to form a female threaded portion 102 and a male threadedportion 104.

The male threaded portion 104 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.3%. The first metallic layer 108 has amean thickness of 7.3 μm.

The metallic layer 108 of the male threaded portion 104 is coated with apassivation layer 110, as described above. By definition, thepassivation layer has anti-corrosive properties.

Optionally, the passivation layer 110 of the male threaded portion 104is coated with a barrier layer 114 as described above, which also hasanti-corrosive properties.

The substrate 100 of the female threaded portion 102 has a surfaceroughness. The surface roughness has been obtained by a sand blastingprocess. In the exemplary embodiment of FIG. 4, the surface roughness(Ra) is approximately 2 μm. In a variation, the sand blasting processmay be carried out on the metallic anti-corrosion and anti-galling layer108 of the female threaded portion 102 described below.

The female threaded portion 102 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.8%. The metallic layer 108 has a meanthickness of 7.7 μm.

As mentioned above, a sand blasting process may be carried out on themetallic layer 108 of the female threaded portion 102. In one embodimentof the invention, the metallic layer 108 has a surface roughness (Ra) ofapproximately 2 μm. This means that the passivation layer or thelubricant layer 112 described below can adhere well.

The metallic layer 108 of the female threaded portion 102 is optionallycoated with a passivation layer 110, as described above. By definition,the passivation layer has anti-corrosive properties.

The passivation layer 110 of the female threaded portion 102 is coatedwith a lubricant layer 112. In the embodiment of FIG. 4, the lubricantlayer is constituted by epoxy and MoS₂.

In a variation, it is possible for there to be no passivation layer 110and to apply the lubricant layer 112 directly to the metallic layer 108of the female threaded portion 102 (or directly to the metallic layer108 of the male threaded portion as appropriate).

Example 5

FIG. 5 shows a substrate 100 formed from steel. The substrate 100 isshaped so as to form a female threaded portion 102 and a male threadedportion 104.

The substrate 100 of the male threaded portion 104 has a surfaceroughness. The surface roughness has been obtained by a sand blastingprocess. In the exemplary embodiment of FIG. 5, the surface roughness(Ra) is approximately 2 μm. In a variation, the sand blasting processmay be carried out on the metallic anti-corrosion and anti-galling layer108 of the female threaded portion 102 described below.

The male threaded portion 104 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.7%. The metallic layer 108 has a meanthickness of 7.2 μm.

As mentioned above, a sand blasting process may be carried out on themetallic layer 108 of the male threaded portion 104. In one embodimentof the invention, the metallic layer 108 has a surface roughness (Ra) ofapproximately 2 μm. This means that the passivation layer or thelubricant layer 112 described below can adhere well.

The metallic layer 108 of the male threaded portion 104 is optionallycoated with a passivation layer 110, as described above. By definition,the passivation layer has anti-corrosive properties.

The passivation layer 110 of the male threaded portion 104 is coatedwith a lubricant layer 112. In the embodiment of FIG. 5, the lubricantlayer 112 is constituted by acrylic resin and carbon black.

In a variation, it is possible for there to be no passivation layer 110and to apply the lubricant layer 112 directly to the metallic layer 108of the male threaded portion 104.

The substrate 100 of the female threaded portion 102 has a surfaceroughness. The surface roughness has been obtained by a sand blastingprocess. In the exemplary embodiment of FIG. 5, the surface roughness(Ra) is approximately 2 μm. In a variation, the sand blasting processmay be carried out on the metallic anti-corrosion and anti-galling layer108 of the female threaded portion 102 described below.

The female threaded portion 102 is coated with a metallic anti-corrosionand anti-galling layer 108. The metallic layer 108 has been depositedelectrolytically, as described above. The metallic layer 108 isconstituted by a binary zinc-nickel (Zn—Ni) alloy and contains zinc(Zn), namely a mean amount of 86.2% by weight. The metallic layer 108has a mean thickness of 6.7 μm.

As mentioned above, a sand blasting process may be carried out on themetallic layer 108 of the female threaded portion 102. In one embodimentof the invention, the metallic layer 108 has a surface roughness (Ra) ofapproximately 2 μm. This means that the passivation layer or thelubricant layer 112 described below can adhere well.

The metallic layer 108 of the female threaded portion 102 is optionallycoated with a passivation layer 110, as described above. By definition,the passivation layer has anti-corrosive properties.

The passivation layer 110 of the female threaded portion 102 is coatedwith a lubricant layer 112. In the embodiment of FIG. 5, the lubricantlayer 112 is constituted by an acrylic resin and a dispersion of carbonblack in that resin.

In a variation, it is possible for there to be no passivation layer 110and to apply the lubricant layer 112 directly to the metallic layer 108of the female threaded portion 102 (or directly to the metallic layer108 of the male threaded portion, as appropriate).

In particular embodiments, at least some of the layers may extend overother elements of the threaded portion. As an example, when an abutmentis present on the threaded portion, the layers may extend over it.

The Applicant has carried out comparative roughness tests betweenthreaded portions before electrolytic deposition of a metallic layer inaccordance with the invention and after electrolytic deposition of ametallic layer in accordance with the invention. The roughness wasmeasured in the direction parallel to the direction of machining of saidportions. The results are reported in Table 1.

TABLE 1 Comparison of roughness. Before electrolytic After electrolyticdeposition ZnNi deposition ZnNi Ra Rz Rt Ra Rz Rt Roughness (μm) (μm)(μm) (μm) (μm) (μm) No sand Mean 0.458 2.453 2.453 0.330 2.023 4.316blasting Std Dev n.a. n.a. n.a. 0.166 0.569 3.895 Sand Mean 3.25421.243  21.243  1.495 9.918 11.561 blasting Std Dev 0.171 1.271 1.2710.166 1.127 2.060 Std Dev = standard deviation n.a. = not applicable

Ra is the mean deviation roughness—it is the arithmetic mean of theabsolute values of the distances between the peaks and valleys measuredon the roughness profile. Rz is known as the mean maximum roughness—thisis the mean of the maximum heights measured over several (for example 5)selected portions on a roughness profile. Rt is known as the totalroughness—this is the maximum height measured over the whole of theroughness profile.

Table 1 shows that the samples of threaded portions after electrolyticdeposition have a reduced roughness in the direction parallel to thedirection of machining compared with the samples of threaded portionsbefore electrolytic deposition. In particular, the electrolyticdeposition in accordance with the invention has a levelling effect.

FIG. 6 shows photographs of threaded elements taken with an opticalmicroscope. More particularly, FIG. 6 shows two selected portions of aprior art threaded element compared with two analogous selected portionsof a threaded element in accordance with the invention.

The microscope used was optical. The magnification was: ×500. The scaleindicated on each photograph is 50 μm.

The prior art threaded element is shown in photographs 200 a and 200 b.The prior art substrate 202 formed from steel is coated with a layer 204comprising particles of lamellar zinc dispersed in an epoxy resin. Thelayer 204 was applied using a process which is known in the art. Theprior art process comprises pneumatic spraying of the layer 204 onto thesubstrate 202 at ambient temperature, followed by hot curing of thesubstrate/layer ensemble. During the spraying phase, the composition ofthe layer 204 comprises a solvent. The curing phase is used to eliminatethe solvent and cross-link the layer 204. The photographs 200 a and 200b show that the layer 204 is heterogeneous. In fact, the layer 204 ofthe prior art threaded element has a non-uniform microstructure.

The threaded element of the invention is shown in photographs 300 a and300 b. The substrate 100 is coated with a first metallic layer 108constituted by a binary Zn—Ni alloy of the type described in Example 1above. The binary alloy was applied electrolytically in order to form ahomogeneous layer. In fact, photographs 300 a and 300 b of FIG. 6 showthat the first metallic layer 108 of the threaded element of theinvention has a uniform microstructure. In the present case, it is amonophase gamma (γ) type microstructure.

FIG. 7 shows a photograph 400 of a threaded element in accordance withthe invention taken with an optical microscope. The magnification is:×500. The scale indicated on each photograph is 50 μm.

The substrate 100 was coated with a second metallic layer 106constituted by a binary Zn—Ni alloy of the type described in Example 1above. The binary alloy was applied electrolytically in order to form ahomogeneous layer. The metallic layer had a thickness of approximately 4μm to approximately 6 μm (mean thickness approximately 5 μm). Themetallic layer was coated with a lubricant layer 112 of the hot-meltHMS-3 type, as described in Example 1. The lubricant layer has athickness of approximately 40 μm to approximately 43 μm.

The second metallic layer 106 has a uniform microstructure. In fact, thesecond metallic layer constituted by a binary Zn—Ni alloy also has amonophase gamma (γ) type microstructure.

FIGS. 6 and 7 thus demonstrate that the metallic layer of the inventionhas a uniform microstructure.

The elements of the tubes of the invention, namely the male or femalethreaded portions as well as the connections produced with theseportions, comply with the conditions of international standard API RP5C5 (3^(rd) Edition, July 2003). In particular, the tube elementsresisted 15 makeup/breakout procedures and fully satisfied the sealingconditions.

The elements of the tubes of the invention, namely the male or femalethreaded portions as well as the connections produced with theseportions, were in full compliance with the conditions of Europeanstandard NF EN ISO 9227 relating to saline mist tests. In particular,the tube elements responded positively as regards corrosion resistanceover 1000 h of exposure to an aggressive environment.

The invention claimed is:
 1. A connection assembly, comprising: a maleend portion having a threading and a sealing surface; and a female endportion having a threading and a sealing surface complimentary to themale end portion; wherein the threading and the sealing surface of oneof the male and female end portions are coated with a first metallicanti-corrosion and anti-galling layer comprising zinc as a major elementby weight, said first metallic anti-corrosion and anti-galling layerbeing coated with a first passivation layer comprising trivalentchromium; the threading and sealing surface of the remaining of the maleand female end portions are coated with a second metallic anti-gallinglayer comprising zinc as a major element by weight, said second metallicanti-galling layer being at least partially coated with a lubricantlayer comprising a resin and a dry solid lubricant powder dispersed insaid resin, and at least one of the first and second metallicanti-corrosion and anti-galling layers is obtained by electrolyticdeposition.
 2. The connection assembly according to claim 1, wherein atleast one of said first and second metallic anti-corrosion andanti-galling layers comprises at least 50% by weight of zinc.
 3. Theconnection assembly according to claim 1, wherein at least one of saidfirst and second metallic anti-corrosion and anti-galling layers has athickness in a range of from 4 μm to 20 μm.
 4. The connection assemblyaccording to claim 1, wherein the lubricant layer has a thickness in arange of from 5 μm to 50 μm.
 5. The connection assembly according toclaim 1, wherein at least one of said first and second metallicanti-corrosion and anti-galling layers comprises a substance selectedfrom the group consisting of pure zinc and a binary alloy of zinc ofZn—X, wherein X is selected from the group consisting of nickel, iron,magnesium and manganese.
 6. The connection assembly according to claim1, wherein at least one of said first and second metallic anti-corrosionand anti-galling layers is a binary zinc-nickel alloy wherein a nickelcontent is in a range of from 12% to 15% by weight and wherein a microstructure of the at least one of said first and second metallicanti-corrosion and anti-galling layers is monophase and in a gamma (γ)phase.
 7. The connection assembly according to claim 1, having a secondpassivation layer, comprising trivalent chromium between the secondmetallic anti-corrosion and anti-galling layer and the lubricant layer.8. The connection assembly according to claim 7, wherein, at least oneof said first and second passivation layers is coated with a barrierlayer constituted by a mineral matrix layer comprising particles ofsilicon dioxide.
 9. The connection assembly according to claim 8,wherein the mineral matrix layer further comprises potassium oxide. 10.The connection assembly according to claim 7, wherein at least one ofsaid first and second passivation layers is coated with a barrier layerconstituted by an organo-mineral matrix layer comprising particles ofsilicon dioxide.
 11. The connection assembly according to claim 7,wherein at least one of said first and second passivation layers iscoated with a layer of dry lubricant.
 12. The connection assemblyaccording to claim 1, wherein the dry solid lubricant powder is at leastone selected from the group consisting of a polytetrafluoroethylene, amolybdenum disulphide, a molybdenum dithiocarbamate, a carbon black anda graphite fluoride.
 13. The connection assembly according to claim 12,wherein the resin is an acrylic resin and the dry solid lubricant powdercomprises from 3% to 15% by weight of the carbon black, the molybdenumdisulphide, or the molybdenum dithiocarbamate, alone or in combination.14. The connection assembly according to claim 1, wherein the resin isselected from the group consisting of a polyvinyl resin, an epoxy resin,an acrylic resin, a polyurethane resin and a polyamide-imide resin. 15.The connection assembly according to claim 1, wherein the male endportion further comprises a first abutment and the female end portionfurther comprises a second abutment, wherein the first and secondabutments contact each other.
 16. The connection assembly according toclaim 1, wherein the male and female end portions are steel.
 17. Theconnection assembly according to claim 1, wherein the connectionassembly connects a first drill pipe and a second drill pipe.